Effects of Brittleness on Crack Behaviors in Rock-Like Materials

Abstract The principal objective of this work is to understand the effects of brittleness on crack behaviors in rock, rock-like materials, and the underlying fracturing mechanisms. Brittleness, as one of the critical parameters of rock, significantly affects mechanical properties and fracturing behaviors. A better understanding of the effects of the brittleness on fracturing behaviors can lead to a more satisfactory characterization and assessment of the overall behaviors and performances of rock mass. In this study, experiments on rock-like materials with two parallel preexisting flaws are conducted to study the effects of brittleness, as well as the mechanical properties, crack initiation modes, crack coalescence types, and ultimate failure modes, on cracking behaviors of rock-like materials. We find that the content of the adhesive material’s polyamide and epoxy have a significant effect on the brittleness of rock-like materials that consist of sand, barite, epoxy, polyamide, and alcohol at different mass ratios. The brittleness of specimens decreases with increasing content of the cementing agents epoxy and polyamide. Seven types of crack initiation—wing crack, antiwing crack, coplanar secondary crack, oblique secondary crack, out-of-plane tensile crack, out-of-plane shear crack, and far-field crack—are observed in high-speed images of the ultimate failure crack morphology. Four types of crack coalescence are also identified: tension coalescence mode, shear coalescence mode, and the mixed mode including tension-shear coalescence mode and tension-shear-tension coalescence mode. A primary observation was that the ultimate failure mode is a transition from tension failure mode to tension-shear failure mode and shear failure mode, in sequence, and the rupture angle increases gradually with decreasing brittleness. Finally, the effects of the brittleness on the mechanical properties of rock-like materials, including the complete axial stress-strain curves, crack initiation stress ratio, and residual stress, are investigated in detail.